Health problems are rare in tested Honolulu County wells.
All 7 health checks came back rare here.
From 42 wells tested in Honolulu County since 2000; your own well needs its own test. How to read this
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
About 1 in 163 people 6,214 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
Radon risk (a gas from rock)
Less likely, but the EPA still says test your air.
Radon zones: EPA map
Here's how Honolulu County compares with Hawaii and the counties around it.
All 7 health checks are rare in Honolulu County.
Manganese0 of 40 wells over
Nitrate0 of 40 wells over
Arsenic0 of 36 wells over
Uranium0 of 36 wells over
Radon in water0 of 25 wells over
Lead0 of 36 wells over
Fluoride0 of 40 wells over
Every well needs a bacteria test every year.
No bacteria tests from Honolulu County wells are in the public data. Test every year anyway.
Iron reached staining levels in 0 of 40 tested wells, and it isn't a health risk.
Iron stains0 of 40 wells had it
Most of the 42 wells tested in Honolulu County were last tested before 2010.
An old result shows the water as it was then, so treat these 42 wells as a starting point and test your own.
Most Honolulu County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 3 things to check in Honolulu County.
- Bacteria
- Nitrate
- Arsenic
What Hawaii offers well owners
- Free testingWe didn't find a free program for all of Hawaii. Hawaii's private well page
- Certified labsHawaii's list of certified labs
- Well recordsHawaii's well record search
Here's what we know about radon and PFAS in Honolulu County.
Honolulu County is in the EPA's lowest radon zone, so radon from well water is unlikely to be a problem. Radon guide
Between 2023 and 2025 the EPA had 19 town water systems in Honolulu County test for PFAS. 2 found some PFAS, all below the new limits. No well in Honolulu County has public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in Honolulu County
Is well water in Honolulu County safe to drink?
Most tested wells in Honolulu County came in under the limits. Of 7 health checks with enough tests, nitrate came closest, at 0 of 40 wells over. Every well is different, so test yours for bacteria, nitrate and arsenic.
Where can I get my well tested in Honolulu County?
Use a lab Hawaii has certified for drinking water. Hawaii's list is linked above, in the box about testing. Ask for bacteria, nitrate and arsenic, the tests that matter most in Honolulu County.
How often should I test my well in Honolulu County?
Honolulu County has no public bacteria results for wells, so follow the CDC's advice: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
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Where the Honolulu County numbers come from
- People on wells: 6,214 in Honolulu County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 298 well water samples from 42 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2014.
- PFAS: EPA tests of 19 town water systems in Honolulu County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Honolulu County is zone 3 on the EPA Map of Radon Zones.
- State programs and links: Department of Health, Safe Drinking Water Branch, checked November 1, 2026.